The present invention relates to a method for picking up an image with high-resolution, and apparatus therefor. More specifically, the invention relates to a high-resolution image pickup method and apparatus therefor for enhancing the resolution of image pickup systems which are used for automatically deciding the conformity of inspection results in the production line with respect to inspections for point defects and the like on display devices used in electronic equipment and other fields, such as liquid crystal panels, shadow masks, CRT panels and plasma displays.
As a method for reading the screen displayed on a display device, there has been provided, as a primary method, one using a CCW area sensor, which is a two-dimensional sensor.
In this method, pixels arrayed in columns and rows of two-dimensional sensors and pixels arrayed in columns and rows of a display device are associated with each other (hereinafter, unless otherwise specified, pixels of the display device will be referred to as "display pixels", and pixels of the sensors will be referred to as "sensor pixels"), where the pixel arrangement is generally such that a plurality of sensor pixels are associated with one display pixel.
This is explained by taking a case of a display device of 3000.times.1000 pixels of a liquid crystal panel as an example. A liquid crystal panel includes display portions and non-display portions of the pixels. Point defects in the lighting inspection for these display portions can be classified into dark dots, which are a group of display pixels that will not make display in the displaying state of the liquid crystal panel, and bright dots, which are a group of display pixels that will make display in the non-display state. For an automatic inspection apparatus for inspecting these point defects, it is required to determine the correct positions of these point defects in the display device. In this case, when two sensor pixels are assigned to one display pixel, approximately 6000 pixels are required in the row direction.
However, it is not easy to increase the sensor pixels to meet the increasingly growing requirement of high-density pixels of liquid crystal panels. This is due to increases in the probability of defects of the sensor pixels themselves in the semiconductor manufacturing process, which is caused by the increase in the number of sensor pixels. For this reason, it would be the case to use a CCW area sensor with a low number of sensor pixels, where even such a method could not allow the required automatic inspection apparatus to be implemented. As the method of using a CCW area sensor with a low number of sensor pixels, there have conventionally been available a method of using a plurality of CCD area sensors in the first place, and a method of moving the relative positions of the CCD area sensor and the inspection subject in very small steps (for example, see a paper "Automatic Inspection Technique for LCD Display Image Quality" in the journal, "Monthly LCD Intelligence", issued March 1996, pp. 66-75).
However, the aforementioned two conventional methods have had the following issues.
First, in the first method of using a plurality of CCD area sensors, it would be difficult to align the image pickup optical systems of the inspection apparatus, and besides it would become complicated to treat the overlapped portions of image pickup portions of display pixels, which are the inspection subject, of each other image pickup sensors. Thus, this is not a method that will not desirably be employed. Also, when the CCD area sensor is very expensive, using a plurality of CCD area sensors would result in a very high-price image pickup system on the whole.
In the second method of moving the relative positions of the CCD area sensor and the inspection subject in very small steps, since the number of pixels of the CCD area sensor is not increased, it could not be expected to greatly improve the resolution. For example, there may be a case where the number of display pixels would be increased, resulting in such a setting of magnification that display pixels 51 are small relative to sensor pixels 50 as shown in FIG. 7, where the display pixels are assigned to the sensor pixels. This is a case where the image pickup sensors count 1000 pixels in the row direction, while the display pixels count 2000 pixels in the row direction. In this case, even if the relative positions of the CCD area sensor and the inspection subject are moved in very small steps, it would be impossible to obtain information unique to the display pixels because only one image pickup sensor is assigned to two display pixels.